1. Field of the Invention
The present invention relates to an information recording medium of the type suitable for use with an optical video disk, a digital audio disk, or the like.
2. Description of the Prior Art
At the present time, optical video disks, digital audio disks, and the like, have already been put into practical use. In general, in disks of this type, the user employs a disk only in reading out the information which has previously been recorded thereon. Recently, various information recording media have been proposed which would allow the user to write or record desired information on the medium. These information recording media, however, are not yet in widespread use.
The previously proposed information recording medium capable of recording information utilizes as its recording material layer a thin metal film having a low melting point and composed, for example, of bismuth and tellurium. This thin metal film is irradiated with a laser beam in response to the information signal and then melted. In the melted portion of the thin metal film, record pits are formed by apertures or recesses as the mechanical change of shape occurs and the information is thus recorded. However, when the information recording is being carried out with the formation of the record pits as mentioned, a large amount of power is required to carry out the recording of information by melting of the recording layer. Moreover, it is difficult to control the shape of the recorded pits formed by the melting so that the noise level becomes high and the resolution becomes low. Also, it is difficult in this way to carry out high density recording.
The assignee of the present application has previously proposed an information recording medium which can perform information recording on the basis of a change of optical characteristics of the recording medium. Such a disclosure will be found, for example, in the copending application of Watanabe, Ser. No. 361,384, filed Mar. 24, 1982 and assigned to the same assignee as the present application, and issued as U.S. Pat. No. 4,460,636 on July 17, 1984.